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Oceans are warming up, and there should be no controversy about it

New research confirms that there wasn't a pause on global warming in the oceans — only a change in measurements. This confirms findings from the US National Oceanic and Atmospheric Administration (NOAA), and may finally put to rest the controversy about an apparent slowdown in rising global temperatures. The controversy heated up around five years ago, as many scientists, including the International Panel on Climate Change, acknowledged the so-called “global warming hiatus” — the perceived “pause” in rising global temperatures at the beginning of the 21st century. The slowdown was particularly apparent in ocean temperatures. Scientists struggled to explain the data and climate skeptics pointed to it as evidence that climate change is a hoax.

“Some people, particularly some US politicians, were using this slowdown to argue that climate science must be wrong, and therefore we don’t need to do anything,” study co-author Kevin Cowtan of University of York, in the UK, tells The Verge. Then in 2015, the NOAA came out with a paper in Science that argued that global warming since 2000 had been underestimated and in fact, there was no detectable slowdown in ocean warming between 1998 and 2012. In that study, NOAA showed that the oceans have actually warmed 0.12 degrees Celsius (0.22 degrees Fahrenheit) per decade since 2000, instead of 0.07 degrees Celsius per decade as previous estimates had shown. That indicated a higher rate of warming in recent years.

The confusion was due to a change in the way ocean temperatures are measured. Until the early 1990s, temperatures were measured with ships, says study co-author Zeke Hausfather of Berkeley Earth, a non-profit research institute focused on climate change. Sea water was automatically piped through the ship’s engine room, where the measurement took place. But engine rooms are typically warm and this skewed the results. In recent years, measurements have increasingly been taken by buoys, which are in direct contact with the ocean water. Buoys do report slightly cooler water temperatures, but that’s only because the sea water is not piped through a warm engine room first. When adjusted for this “cooling bias,” scientists can see that oceans are warming up.

The 2015 NOAA study caused a huge political controversy in the US. Climate deniers accused the federal agency of doctoring the results. The House Committee on Science, Space, and Technology even subpoenaed NOAA head Kathryn Sullivan, asking her to turn over records and internal communications. (Sullivan refused to turn over scientists’ emails.) “It became quite a big political hot potato,” Hausfather says in a video released with the study.